Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1997-10-24
2003-02-11
Moe, Aung S. (Department: 2712)
Television
Camera, system and detail
Combined image signal generator and general image signal...
Reexamination Certificate
active
06519001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is useful in color signal processing. It consists of a color signal separating circuit using a color signal separating algorithm.
2. Description of the Related Art
A digital signal processing camera using a CCD area image sensor (hereinafter referred to as a CCD) converts an image signal composed of light into an electrical signal representing the original image. It then performs predetermined signal processing on the electrical signal. Next, it saves the processed signal in a storage medium such as an analog video tape recorder or digital video tape recorder so that the electrical signal can be reproduced when necessary. There are two kinds of CCDs: one is for black-and-white signal processing, and the other is for color signal processing. Based on the CCD they contain, cameras are divided into groups of black-and-white or color, and each type employs different basic signal processing methods. Black-and-white signal processing is simple since photoelectric conversion requires only one characteristic, the brightness of an image. On the other hand, color signal processing requires luminance signals representing the brightness of an image as well as color signals to keep track of colors.
The present invention is confined to color signal processing. To convert a two-dimensional light image signal into a color signal, there are two methods. First, one can install three primary color filters (red, blue, and green) into a CCD and convert the light image into an electrical signal. Second, one can install a prism, obtain three primary red, blue, and green colors, and then convert each resulting light image into electrical signals. In the latter, color separation is excellent, although the size of a camera is increased due to the need for a prism and three black-and-white CCDs. On the other hand, the former has disadvantages in that it is difficult to build due to the increase of CCD pixels. It also suffers from poor color reproduction quality due to uniformless red, blue, and green filter characteristics. However, it has the advantage of creating small cameras. To get the best of both methods, single CCD cameras have been widely used recently. They process a image signal with a single CCD, then use a complementary color filter exhibiting excellent filter characteristics.
A conventional color signal separating technology using a complementary color filter will be described referring to
FIGS. 1 and 2
.
FIG. 1
illustrates a CCD complementary color filter array.
Referring to
FIG. 1
, the complementary color filter array includes magenta (MG) composed of red (R) and blue (B) signal components; yellow (YE) composed of red and green (G) color signal components; cyan (CY) composed of blue and green signal components; and a green signal G. Signals read from the complementary color filter array of
FIG. 1
are divided into even fields and odd fields.
FIG. 2
is a timing diagram of output signals of a CCD having the complementary color filter array shown in FIG.
1
.
Referring to
FIG. 2
, S
2
(=MG+YE) and S
1
(=G+CY) are sequentially output from an odd line of an odd field, while S
2
(=G+YE) and S
1
(=MG+CY) are sequentially output from an even line of the odd field. In addition, S
2
(=G+YE) and S
1
(=MG+CY) are sequentially output from an odd line of an even field, and S
2
(MG+YE) and S
1
(G+CY) are sequentially output from an even line of the even field. To reiterate, in the even field a signal component stored in each pixel is output as synthesized MG+YE and G+CY in the even line, and as synthesized G+YE and MG+CY in the odd line, by the complementary color filter defined by a field interlace method. Symmetrically, in the odd field the signal is output as synthesized G+YE and MG+CY in the even line, and as synthesized MG+YE and G+CY in the odd line. This is a formal format regulated in a CCD structure, and defines an interlace signal processing method. The signals generated above are the fundamental inputs to the color signal processing algorithm of a color camera.
In conventional color signal separating technology, the above four signals are separated into pseudo color signals and luminance signals by the following algorithm.
Even
field
,
odd
line
:
S2
-
S1
=
(
G
+
YE
)
-
(
MG
+
CY
)
=
G
+
R
+
G
-
R
-
B
-
G
-
B
=
G
-
2
B
=
-
(
2
B
-
G
)
=
CCB
Even
field
,
even
line
:
S2
-
S1
=
(
MG
+
YE
)
-
(
G
+
CY
)
=
R
+
B
+
R
+
G
-
B
-
G
-
G
=
2
R
-
G
=
CCR
S2
+
S1
=
[
(
G
+
YE
)
+
(
MG
+
CY
)
]
or
[
(
MG
+
YE
)
+
(
G
+
CY
)
]
=
(
R
+
G
+
B
+
G
+
G
+
R
+
G
)
or
(
R
+
G
+
B
+
G
+
G
+
R
+
G
)
=
2
R
+
3
G
+
2
B
=
YL
Though not shown here, CCR and CCB outputs are opposite in an odd field. Necessary red, blue, and green signal components are separated using pseudo color signals CCB & CCR and a pseudo luminance signal YL obtained by the above algorithm. An algorithm for this color separation is given as follows.
Red
=
CCR
+
0.12
YL
=
2
R
-
G
+
0.12
(
2
R
+
3
G
+
2
B
)
=
2
R
-
G
+
0.24
R
+
0.36
G
+
0.24
B
Green
=
YL
-
CR
(
CR
=
CCR
-
CCB
,
here
)
=
2
R
+
3
G
+
2
B
-
[
(
2
R
-
G
)
+
(
2
B
-
G
)
]
=
5
G
Blue
=
-
CCB
+
0.2
G
=
2
B
-
G
+
0.2
H
5
G
=
2
B
A second color separation algorithm is also commonly used for camera signal processing. This algorithm, though using a complementary color filter and the same basic signals output from a CCD, employs a different signal processing method and thus further improves the color quality the electrical image signal relative to the previous algorithm.
MG=R+B
YE=R+G
CY=G+B
G=G
C
1
=MG+YE=2R+B+G
C
2
=G+CY=2G+B
C
3
=MG+CY=2B+R+G
C
4
=G+YE=2G+R
Red
=
C1
-
SR
H
C2
=
2
R
+
B
+
G
-
0.5
(
2
G
+
B
)
=
2
R
+
0.5
B
Blue
=
C3
-
SB
H
C4
=
2
B
+
R
+
G
-
0.5
(
2
G
+
R
)
=
2
B
+
0.5
R
Green
=
(
C2
+
C4
)
-
SG
(
C1
+
C3
)
=
2
G
+
B
+
2
G
+
R
-
0.33
(
2
R
+
B
+
G
+
2
B
+
G
)
=
4
G
+
B
+
R
-
0.33
(
3
R
+
3
B
+
2
G
)
=
4
G
-
0.66
G
+
0.01
B
+
0.01
R
=
3.34
G
+
0.01
B
+
0.01
R
The above algorithm is advantageous in that color quality is improved, when compared to the first algorithm, by intersectionally operating on adjacent signal components. Unfortunately, in the above two algorithms other components are included in the basic signals red, blue, and green. These cause the phase of a color to vary during formation of three important signals generated in subsequent stages: color difference, white balance, and hue control. The net result of this is unintended colors. Moreover, in the above conventional algorithms, differences made between luminance signals by the filter causes the incorrect reproduction of red and blue signals. Finally, due to the prior mentioned luminance signal difference, the level of a green color signal varies as the basis for generating red, green, and blue color signals at every line. This decreases the color quality of green.
SUMMARY OF THE INVENTION
Digital cameras use CCD image sensors to transform images from light waves into electrical signals. There are two
Marger & Johnson & McCollom, P.C.
Moe Aung S.
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